Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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TITLE: PHOTO SENSOR ARRAY FOR BANKNOTE EVALUATION
FIELD OF THE INVENTION
The invention relates to a photo sensor array for
banknote evaluation as well as a method of banknote
evaluation. In particular the photo sensor array
illuminates the banknote as it moves past the sensing
arrangement and information is gathered from at Least 750
of the banknote surface.
BACKGROUND OF THE INVENTION
Banknote evaluation is now commonly carried out
and has become more critical in that the technology
available to produce counterfeit bills is easily
available and the quality of counterfeit bills has
significantly increased. Currency of major countries
continues to add different security features to their
banknotes so that fraudulent banknotes are more easily
detected and to act as a deterrent to the production of
counterfeit bills.
Unattended currency accepting equipment such as
vending machines, token dispensing machines, and other
automated equipment include banknote acceptors. The
banknote acceptors transport banknotes along 'an
evaluation path and conduct various tests to predict the
authenticity thereof. These banknote acceptors typically
include optical sensors having an illumination source for
illuminating a particular strip of the banknote as it
moves through the evaluation path. The optical sensors
include detectors for evaluating reflected light and can
include filtering for light evaluation at different
frequencies.
Banknote acceptors typically include a series of
optical sensors that evaluate strips of a banknote to
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detect different security features provided at different
positions on the banknote. Such evaluators often include
different sensors for determining the magnetic,
electrostatic, transparency and other characteristics of
the banknote. Such banknote acceptors include sufficient
optical sensors for evaluating critical aspects of
different denominations of banknotes to be received and
as such, the optical sensors are placed at different
points across the evaluation path. There is a compromise
between the number of sensors used to scan the surfaces
of the banknote and the cost of the banknote acceptor.
Full scanning of the banknote surface provides more data
and can improve the prediction of whether the banknote is
authentic or not, but the additional cost is difficult to
justify, and furthermore, there is a time restraint for
the effective analysis of the data.
Typically if the banknote moves slower along the
banknote evaluation path or more time is provided to
allow the banknote acceptor to consider all of the data,
improvements in the prediction can be obtained.
Unfortunately, from a customer point of view, the
evaluation process must be essentially completed in real
time; otherwise the transaction may be discontinued. In
some applications it may be more profitable to accept
additional risk in accepting a counterfeit banknote as
opposed to an increase in the transaction time and
improved evaluation of the banknote.
A further problem associated with existing
banknote evaluation systems involves variations in the
placement of the banknote within the evaluation path.
The banknote can be fed to the evaluation path at a
slight angle and/or the evaluation path can be larger
than the width of the banknote and thus, the precise
position of the strip being illuminated is within a range
but is not precisely known. These factors also affect
the accuracy of the banknote evaluation.
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There continues to be a need to provide effective
banknote evaluation quickly and at an acceptable cost.
The present invention provides an effective
solution that addresses a number of these issues.
SUMMARY OF THE INVENTION
A method of banknote evaluation according to the
present invention comprises moving a banknote along an
evaluation path past an optical sensing arrangement where
the precise location of the banknote, relative to the
optical sensing arrangement is not known. The method
includes using the optical sensing arrangement to
generally illuminate the banknote as it moves past the
sensing arrangement and focusing reflected light from the
illuminated banknote surface onto a photo array to
provide a strip analysis corresponding to at least 750 of
the banknote surface.
The strip analysis contains at least 50 divisions
and the strip analysis is used to determine the position
of the banknote relative to the optical sensing
arrangement. Once the position is known, the at least 50
divisions are selectively used to evaluate the
authenticity of the banknote relative to a standard.
With this arrangement, improved analysis is possible as
the relatively position of the 50 divisions within to the
width of the banknote is known and it is not necessary to
have the substantial tolerances necessary when the
precise position of the banknote is not known.
According to an aspect of the invention, the
method includes evaluation of an angle of the illuminated
banknote relative to the optical sensing arrangement in
selecting the divisions used in the evaluation of the
banknote for authenticity.
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In a different aspect of the invention, the
reflected light is focused onto a photo array having at
least 64 pixels and each pixel forms a division.
In a further aspect of the invention, the
illuminating step associated with the optical sensing
arrangement illuminates across a width of the evaluation
path such that 100 of the surface of the banknote facing
the optical sensing arrangement is illuminated and the
photo array receives reflected light across the width of
the evaluation channel.
In a further aspect of the invention, the full
illumination of the banknote surface is used to determine
the edge regions of the banknote relative to the photo
array and the evaluation uses only the divisions
representing a response from the banknote.
In a further aspect of the invention, the step of
focusing includes at least three lenses to converge the
reflected light onto the photo array.
In a further aspect of the invention, the step of
selectively using the at least 50 divisions includes a
series of evaluations of different divisions that vary
according to the determined position of the banknote.
BRIEF DESCRIPTION OF THE DRAWINGS
Preferred embodiments of the invention are shown
in the drawings, wherein:
Figure 1 is a side view through a banknote
evaluation path illustrating the photo sensor array and
lens arrangement;
Figure 2 is a top view of the photo sensor array
and lens arrangement;
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Figure 3 is a sectional view showing additional
details of the final converging lens;
Figure 4 is a sectional view through an alternate
final lens converging arrangement; and
Figure 5 shows a further variation of one of the
deflectors shown in Figure 1.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The optical sensing arrangement 2 shown in Figures
1 and 2 provide details of the various components and
their position relative to the banknote evaluation path
12. A banknote 14 is being advanced past the evaluation
position generally shown as 17 and the upper surface 16
of the banknote is being illuminated.
The various components are secured on the PCB
board 4 and includes the light emitting LCDs shown as 6.
As can be appreciated, the evaluation of banknotes is
carried out at different frequencies, and therefore,
different LCDs can be provided for fully illuminating
across the width of the banknote 14, and across the width
of the evaluation channel at the evaluation strip 17.
Certain LCDs may focus on a certain strip region of the
banknote whereas the detector receives a response from
across the width of the evaluation path. Various
arrangements for this illumination of the banknote and
the evaluation channel can be provided. In this case,
focusing optical member 8 receives the light of the LCD 6
and appropriately illuminates the banknote 14 across its
width. The light passes through the window 10 in the
banknote evaluation path 12. It can be appreciated this
window can also provide a desired focusing or
distribution of the emitted light.
Other arrangements for illumination of the
banknote can be provided.
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The exact position of the banknote 14 across the
width of the evaluation channel 12 is typically not
precisely known. Some tolerance in this position is
provided to simplify feeding of the banknote into a
banknote acceptor and the width of a banknote may vary
depending upon the particular currency. Furthermore, as
shown in Figure 1, the exact position of the banknote
relative to the optical sensing arrangement 2 can also
vary. The banknote 14 is typically moved past the
optical sensing arrangement 2 as indicated by the
direction of banknote travel 18. The position of the
banknote in the height of the evaluation path varies as
the banknote can include crease lines etc. and the path
is oversized to reduce the possibility of jamming.
The present optical sensing arrangement 2 focuses
the reflected light from the evaluation strip 17 onto the
photo sensor array 30. The initial reflected light
passes through the window 10 to the converging deflector
36 which directs the reflected light towards the
converging deflector 34 which redirects the light towards
the objective lens 32. The objective lens 32 then
focuses the light on the photo sensor array 30.
As shown in Figure 2, each of the converging
deflectors 34 and 36 converge the light and these
deflectors are placed on the PCB board 4 at a spaced
distance one from the other, effectively along the length
of the banknote evaluation path to allow effective
converging of the light while maintaining the quality
thereof.
The photo sensor array 30 receives light from
across the banknote evaluation path and this light is
provided along the length of the photo sensor array 30.
The upper surface of the banknote 16 reflects light which
is initially reflected and converged by the deflector 36.
This deflector can be a prism member as shown in Figure 1
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but also preferably, starts the converging of the light
as indicated in Figure 2. The converging of the light is
continued by the second converging deflector 36.
The photo sensor array 30 is one of the components
that substantially contributes to the cost of the sensor
arrangement, therefore, the number of pixels of the photo
sensor array is a trade-off with respect to costs. A
photo array having 64 pixels or 128 pixels has proven to
be effective.
The first converging deflector 36 has a length
almost equal to the width of the path and receives light
from the width of the path. In contrast, the second
converging deflector 34 is of a shorter length and this
member returns the light towards the photo sensor array
30.
Figure 3 shows details of the objective lens 32
and the aperture 40 cooperating with the lens to direct
light onto the photo sensor array 30. This arrangement
allows a viewing angle of approximately 60 degrees and
the aperture member 40 effectively limits undesirable
light from the photo sensor array 30.
As can be appreciated, the dimensions of the
various optical components and their ability to converge
and focus the light from the evaluation path onto the
photo sensor array 30, determines the amount of
separation between the different lenses and also
contributes to the cost of the sensor.
Figure 4 shows a more complex final lens
arrangement which includes the additional optical element
42. With this arrangement, the viewing angle is
approximately 80 degrees.
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Figure 5 shows a further aspect that can be used
regarding the initial deflector 36. In this case,
surface 52 which is facing the banknote has been provided
with a concave surface to limit the width of the
evaluation strip 17. As can be appreciated from the
earlier description, the reflected light is being
converged and effectively focused along the length of the
photo sensor array 30. Accurately locating the strip
being evaluated within the photo sensor array provides
better data for evaluation. As can be appreciated, the
evaluation of the light signal provided to the photo
sensor array is sampled as the banknote moves along the
banknote evaluation path and analysis of better located
data, based on the response of a selected group of the
divisions allows for improved accuracy and/or more
frequent sampling.
The full illumination of the banknote 14 is
particularly advantageous in that it is possible to
detect the leading and trailing edges of the banknote as
well as the side edges of the banknote and position the
banknote in the length of the photo sensor array 30. In
this way, the response from the different pixels of the
photo sensor array can be more accurately identified
across the width of the banknote and therefore, the
evaluation software that compares these with standards
can be improved. Much of the previous software
associated with optical sensors was less accurate as the
position of the strip being illuminated could not be
precisely determined and was oversized. Therefore, a
higher tolerance was required with respect to determining
a match in that the response may not become a perfectly
aligned banknote. With the present arrangement, the
edges of the banknote can be determined and the response
from the appropriate divisions of the optical sensor
array 30 can be used for comparing against the standard.
Furthermore, different portions of the response from the
photo sensor array can be used to evaluate other security
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features including water marks, for example. It is also
possible to provide effective comparisons between two or
more different strips along the banknote as their
positions are effectively known. Basically, the photo
sensor array 30 allows more accurate determination of
different portions of the banknote or determination of
the location of the banknote within the evaluation path.
The response of the photo array from the appropriate
divisions is then used. Sensing of a banknote edge is
desirable but other arrangements are possible for
locating of the banknote.
As can be appreciated, the system is based on a
photo sensor array and consists of several optical parts
that focus light reflected from the banknote and focused
onto the pixels of the array. The light that impinges
upon each of the pixels is from a corresponding small
area of the banknote surface. The system preferably
allows collection of information from the full width of
the banknote for more accurate evaluation. With this
arrangement, it is possible to provide optical sensor
arrangements on both sides of the bill and cross
comparisons can also be made.
In the embodiment of Figures 1 and 2, one or two
rows of light emitting diodes 5 can cooperate with the
optical elements 8. They are effectively used to direct
light from the LEDs to the banknote surface such that the
light is essentially uniformly distributed. Different
types of LEDs can be used and the LEDs can be of
different wavelengths and alternately used or cyclically
used one after the other. Therefore, the illumination
system can vary considerably depending upon the
particular banknotes to be evaluated and the accuracy
necessary.
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Sensing of the leading edge also allows accurate
assessment at different points in the length of the
banknote.
A series of optical lenses and deflectors focus
light from the banknote to the pixels of the photo sensor
array. The light that impinges upon the individual
pixels is from only a corresponding small area of the
banknote surface. The various optical members provided
between the banknote and the photo sensor array 30
cooperates to reduce the overall size of the system while
providing effective scanning across the width of the
banknote evaluation channel.
The lens arrangement immediately in front of the
photo sensor array 30 can either include one lens
MENISCUS objective with the MENISCUS made of an organic
glass, for example, polycarbonate. It is also possible
to use the two lens asymmetric objective where both
lenses are made of the same organic glass. With the
first lens, the aperture 40 allows a viewing angle of
approximately 40 degrees, assuming the photo sensor array
has 128 pixels. The two lens system with the restricting
aperture therebetween, can provide a vision angle of 60
degrees.
The first deflector 36 is a total reflection prism
with an angle of reflection of 90 degrees. The second
deflector 34 reflects the light 180 degrees and returns
it towards the photo sensor array 30. Due to convergence
from the first reflector arrangement, the second
deflector is only of a length of about half of the
pathway width.
With this system and the full illumination of the
banknote, for each sample of the signal from the photo
sensor arrays, the edge of the banknote can be determined
and the evaluation of the response from the photo sensor
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arrangement can thus be limited to the particular areas
of interest in the banknote by selecting the appropriate
pixels to consider.
The system is also capable of selecting which
pixels should be considered active pixels. The exact
position of the banknote within the evaluation channel
does vary and this system allows accurate determination
of the active pixels to be compared with the previous
samples and the following samples. The active pixel need
not be the same for the full length of the banknote and
in fact, will probably change. This would be true for a
banknote at an angle, for example. The active pixel
tracking and determination of the active pixels under
evaluation provides improved accuracy and simplifies the
comparison with the standard response.
The system also allows for evaluation of certain
features that may be provided only on a certain segment
of the banknote. For example, a watermark may be
provided on a bottom right corner and this system can
effectively use the response from the photo sensor array
for that portion and when the watermark is illuminated
whereby the quality of the watermark can be assessed.
25 This is in contrast to a sensor that is of a very limited
width where only a portion of the watermark would be
illuminated. As previously mentioned, the light emitting
diodes can also be controlled to allow more effective
evaluation of these selected portions.
A further aspect of the invention is that security
features do not necessarily run in a parallel manner to
the edges of a banknote. For example, a security
feature may be provided at an angle across a banknote.
With the present invention, the evaluation of the
different pixels corresponding to angle and position in
the length of the banknote can be evaluated. This is
possible as the front edge and the side edges are sensed
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within the width of the path and the appropriate pixels
to be considered can be determined. Any changes in the
position of the angle of the banknote as it moves through
the evaluation channel is also taken into account as the
side edge determination can be made for each sample.
A further aspect of the invention is with respect
to identifying a particular technique sometimes used in
an attempt to defeat the system. It is known to attach a
string like member to a banknote to allow withdrawal of
the banknote once the banknote acceptor has determined
the banknote to be authentic. Strip analysis of
banknotes allows a clever individual to appropriately
attach the string like member to a portion of the
banknote that will not be evaluated. With the present
full illumination of the banknote evaluation channel and
the detecting of the edges of the banknote, such a string
like member can easily be identified.
As previously considered, the present system
allows exact detection of the front and back edges of a
banknote and this allows synchronization of the
measurement process with the current location of the
banknote in the evaluation channel. With the full
banknote illumination possible with the present
arrangement, separate sensors for detecting the leading
and trailing edges of a banknote are not required.
Furthermore, the full illumination allows proved accuracy
of the identification of these edges, as well as
providing full information regarding the selective use of
the full scan of the banknote.
Although various preferred embodiments of the
present invention have been described herein in detail,
it will be appreciated by those skilled in the art that
variations may be made thereto without departing from the
spirit of the invention or the scope of the appended
claims.
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